The following background description constitutes a description of the background to the present invention, which does not, however, necessarily constitute prior art.
Vehicles, such as for example cars, buses and trucks are driven forward by an engine torque produced by an engine in the vehicle. This engine torque is provided to the vehicle's driving wheels through a powertrain in the vehicle. The powertrain contains a range of inertias, torsional compliances and damping components. This means that the powertrain, to a varying degree, may have an impact on the engine torque being transferred to the driving wheels. Thus, the powertrain has a torsional compliance/flexibility and a play, which means that oscillations in torque and/or revolutions, so called powertrain oscillations, may occur in the vehicle when the vehicle, for example, sets off once a torque has been requested from the engine. These oscillations in torque and/or revolutions occur when forces, having been built up in the powertrain in the period between the engine providing the torque and the vehicle moving off, are released as the vehicle moves off. Powertrain oscillations may make the vehicle rock longitudinally, which is described in further detail below. These rocking movements in the vehicle are very disruptive for the driver of the vehicle.
Therefore, in some prior art solutions for avoiding these powertrain oscillations, preventive strategies have been used at the request of the engine torque. Such strategies may utilize limiting torque ramps when the engine torque is requested, whereat these torque ramps have been adapted so that the requested engine torque is limited in such, that the powertrain oscillations are reduced, or do not occur at all.
The torque ramps that are used today when an engine torque is requested thus introduce a limit to how the torque may be requested from the engine in the vehicle. This limitation is necessary under the solutions of prior art, in order to reduce the disruptive powertrain oscillations. Allowing the driver and/or, for example, a cruise control to freely to request a torque would, with current art systems, often give rise to considerable and disruptive powertrain oscillations, which is why limiting torque ramps are used.
The limiting torque ramps in current art are normally static. Static torque ramps, which may also be termed static torques, have an advantage in that they are of a very limited complexity, which is one of the reasons why they are so often used. However, static torque ramps have a number of disadvantages, relating to the fact that they are not optimized to all driving events to which the vehicle may be exposed. For certain driving modes, the static and limiting torque ramps give rise to a reduction in vehicle performance, as, due to the torque ramp, the requested torque is unnecessarily low for driving modes, wherein it would have been possible to request more engine torque without the occurrence of powertrain oscillations. For other driving modes, the torque ramp does not limit the requested torque sufficiently, which means that powertrain oscillations occur and therefore rocking movements in the vehicle. Therefore, the use of torque ramps, for certain driving modes, provides non-optimal torques, which may give rise to an unnecessary reduction in vehicle performance and/or rocking that reduces the comfort, caused by powertrain oscillations.